CZ126897A3 - Steel for producing moulds for plastics, which can be repaired by building-up - Google Patents

Abstract

Low alloy steel comprises by weight 0.17-0.27% carbon, 0.002-0.015% boron, 0.005-0.2% aluminium and up to 0.5% silicon, 2% manganese, 2% nickel, and 3% chromium, also molybdenum, tungsten, vanadium, niobium and tantalum wherein Mo+W/2 = 0-1.5% and V+Nb/2+Ta/4 = 0-0.5%. The proportions are also governed by the following equations: L=Cr+3 (Mo+W/2)+10 (V+Nb/2+Ta/4) omega 2.1; R=3.8 C+10 Si+3.3 Mn+2.4 Ni+1.4 (Cr+Mo+W/2)11;Tr=3.8 C+1.1 Mn+0.7 Ni+0.6 Cr+1.6 (Mo+W/2)+0.6 omega 3; and (Mo+W/2) is more than 0.7% if Cr does not exceed 1.5%. Also claimed are the use of the steel to make, preferably by casting, a mould for injection moulding of plastics and a wire made of the steel for welding or making welding electrodes.

Description

(57)

Steel for the manufacture of molds, in particular molds for injection molding, of a chemical composition such that the% by weight of the carbon content is greater than or equal to 0.17% and less than or equal to 0.27%, the silicon content is less than or equal to 0.5 %, manganese content less than or equal to 2%, nickel content less than or equal to 2%, chromium content less than or equal to 3%, boron content greater than or equal to 0.002% less than or equal to _.

0,015%, aluminum content greater than or equal to 0,005% and less than or equal to 0,2%, sum of molybdenum and half of tungsten content less than or equal to 1,5%, sum of vanadium content and half of niobium content and quarter of tantalum content, or and may contain up to 0.2% sulfur and / or selenium and / or tellurium, titanium and / or zirconium, the sum of the titanium content and half of the zirconium content being less than or equal to 0.3%, up to 0.2% % lead and / or bismuth, up to 0.1% calcium, the remainder being iron and impurities associated with production, the chemical composition also corresponds to the following formula: Cr + 3x / Mo + W / 2 / +

10x / V + Nb / 2 + Ta / 4 / δ 2.1 Mo + W / 2 0.7 when protoplasts. —Reparable

Steel for production of molds by welding.

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The present invention relates to low-alloy steel, especially made for the manufacture of molds for plastics or rubber, which exhibits good welding repair properties.

BACKGROUND OF THE INVENTION

Molds for plastics or rubber are manufactured by machining massive metal blocks the thickness of which may be greater than 1500 mm. The purpose of the machining is in particular to create a cavity having the shape of the object to be cast. In most cases, the surface of the cavity is either polished or chemically treated to further improve the surface of the casting article. Since the casting operation is carried out by injection of hot plastic under pressure, the mold must withstand the forces exerted by the plastic pressure without breaking and must draw heat from the plastic on reuse during friction of the plastic on the surface of the cavity. Steel made for the manufacture of such molds shall have characteristics which enable these requirements to be met. Another property of such steel is the stability of the molds in use, i.e. they must be insensitive to temperature cycles during forming operations.

In addition to the above properties, a certain weldability is required in the mold steel, in order to be able to modify the mold either in case of wear damage or in the shape of the cavity. Generally, when a mold is manufactured for the manufacture of a new product, a first mold is produced for the first products, which is given to its designer, whereby the designer often changes the shape of the article and hence the shape of the cavity has to be more or less modified. In order not to have to produce a new mold again, which is very expensive, the shape of the mold cavity is modified by welding and thus no reworking is required, often supplemented by polishing and preferably chemical treatment. For this reason, it is desirable that the treatment zone and the heat treatment zone (ZAH) exhibit properties that are very similar to those of the parent metal. ____________ _______________________

In order to achieve all these conditions, it would be necessary to have a steel which has in particular and at the same time a very high hardness, very good machinability, very good polishability or chemical machinability, good thermal conductivity, very high homogeneity in all these properties even at high thickness and finally good repairability by welding. Such an ideal steel is not known.

Forms are typically made of low alloy steel forgings which are hardenable enough to obtain a martensitic or bainite structure after hardening and annealing, which is hard enough, has a high yield point and good toughness.

The most widespread steels are P20 steel according to AISA standard and steel W1.2311 or W1.2738 according to German Werstoff standard.

P20 steel contains in wt. from 0.28% to 0.4% carbon, from 0.2% to 0.8% silicon, from 0.6% to 1.0% manganese, from 1.4% to 2.0% chromium and from 0 30% to 0.55% molybdenum, the remainder being iron and manufacturing impurities.

W1.2311 and W1.2738 steel contain in wt. from 0.35% to 0.45% carbon, from 0.2% to 0.4% silicon, from 1.3% to 1.6% manganese, from 1.8% to 2.1% chromium and from 0 15% to 0.25% molybdenum; W1.2738 also contains from 0.9% to 1.2% nickel, the remainder being iron and manufacturing impurities.

These steels have good wear resistance and good mechanical properties, but have the disadvantage of being less weldable, making them difficult to repair by welding.

Some of these disadvantages are avoided in steels for the injection molding of plastics molds, in particular in European patent application EP 0 431 557, whose chemical composition in% by weight. is, from 0.1% to 0.3% carbon, less than 0.25% silicon, from 0.5% to 3.5% manganese, less than 2% nickel, from 1.0% to 3.0% chromium, from 0.03% to 2.00% molybdenum, from 0.01% to 1.00% vanadium and less than 0.002% boron; minimal content of harmful impurities, the rest is iron, chemical composition further basically corresponds to the following formula:

BH = 326 + 847.3 X C + 18.3 x Si - 8.6 X Mn - 12.5 X Cr <460

The result of this relationship is that the maximum allowable amount of carbon is 0.238%.

This steel has the advantages of good crack resistance in post-surfacing even in the absence of pre-heating or post-heating, but has the disadvantages of difficult post-surfacing repair treatment, mainly due to the large hardness difference between the repaired and parent metal ZAH region (from 100 to 150 BH). Furthermore, this steel has a relatively low thermal conductivity, which limits its usefulness in mold making.

In fact, the Applicant has found that the commonly used weldability guides are only partially applicable in the repairability of steel for molds by welding. In fact, the term weldability is understood to mean that weldable steel is a steel in which no cracks occur during the welding operation even in the absence of special safety conditions.

In the case of repair of steels for molds by welding, the condition _r * of non-emergence is definitely necessary, but it is not the only one. It is also necessary that the area repaired by welding, as well as the areas affected by heating, can be subsequently treated, polished and chemically processed well. Further, it is often not possible to carry out repair operations by pre-heating or post-heating.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a steel which at once exhibits all the properties required for mold making steel, which is a thermal conductivity that is better than known steels, easy to repair by welding, which makes it possible in particular to obtain good polishability and chemical treatment after welding.

Accordingly, the present invention is based on steel for the production of molds for an injection mold for plastics, the chemical composition of which by weight. is following:

0.17 % < C <0.27 % 0.0 % < si <0.5 % 0.0 % < Mn <2.0 % 0.0 % < Ni <2.0 % 0.0 % < Cr <3.0 % % < Mo + W / 2 <1.5 % <v 4-Nb / 2 + Ta / 4 <' 0.5 0,002 % < (B) <0.015 % 0.005 %. < Al <0.200 %

preferably at least one of the elements sulfur, selenium and tellurium, in the total sum of these elements being less than or equal to 0.2%, preferably at least one of the elements titanium and zirconium, wherein the sum of titanium and half of the zirconium content is less or equal to 0.3%, preferably at least one of the elements is lead and bismuth, in a content where the sum of these elements is less than or equal to

0.2%, _________________________... .....

preferably, the calcium content is less than or equal to 0.1%, the remainder being iron and manufacturing impurities, the chemical composition further corresponding to the following formula (content by weight):

Cr + 3X (Mo + W / 2) + 10X (V + Nb / 2 + Ta / 4) > 2.1

Mo + W / 2> 0.7% when Cr <1.5%

Qu = 3.8 X C + 1.1 X Mn + 0.7 X Ni + 0.6 X Cr + 1.6 X (Mo + W / 2) + 0.6> 3

R = 3.8 x C + 10 x Si + 3.3 x Mn + 2.4 x Ni + 1.4 x (Cr + MO + W / 2) <11

The carbon is preferably in the range between 0.20% and 0.24%, as well as preferably when the chromium is in the range of 1.5% to 2.5%. It is also preferred that the molybdenum is in the range between

0.5% to 1.2%.

The chemical composition can be selected as follows:

BH = 326 + 847.3 x C + 18.3 x Si - 8.6 x Mn - 12.5 x Cr> 460, the production of which has the advantage of increasing the thermal conductivity of the steel, which improves the overall behavior of the cavities without reducing the repairability by welding.

In particular, and in order to obtain very good conductivity, the silicon content must be less than or equal to 0.2% and more preferably less than or equal to 0.1%.

When the steel contains titanium or zirconium, which is desirable, it is preferred that the content (in% by weight) of titanium, zirconium and nitrogen (these elements are always present at least in the form of impurities) is as follows:

0.00003 <(N) x (Ti + Zr / 2) <0.0016.

Under these conditions, when titanium or zirconium is progressively fed to dissolution in the oxidic phase, the number of titanium or zirconium nitrate impurities greater than 0.1 μιη, loaded in an area of 1 mm ^{2 of the} solid state microstructure, is four times less than the sum of the total content % of titanium impurities in the form of nitrides and half of the total content of impurities of zirconium in the form of nitrides, representing thousandths in wt. Very fine nitride impurities have the advantage of refining the microstructure of the ZAH region and increasing its toughness, thereby achieving good weld repairability. Furthermore, a small number of coarse nitride impurities is suitable for machinability and finishing.

The steel according to the invention can advantageously be used for the production of molds for plastics made of cast steel. These molds are in this case produced by casting.

DETAILED DESCRIPTION OF THE INVENTION

The solution according to the invention will be described in greater detail below with reference to the following examples.

In order to achieve a combination of the required characteristics for the manufacture of injection molds, the steel must, in particular, be capable of obtaining a martensitic or

Ί a bainitic structure in the ingot which may exceed 1,500 mm and whose hardness must be greater than 250 BH after annealing to a temperature greater than 500 ° C. For this reason, the steel must have the required hardenability and must therefore contain sufficient alloying elements. However, these alloying elements are detrimental to thermal conductivity. Their content must also be adjusted to obtain suitable hardenability at maximum thermal conductivity (or minimum thermal resistance). Furthermore, the chemical composition of the steel has a considerable influence on the replaceability by welding and the components must be selected with this in mind on average.

Weld repairability may be affected in particular by the hardness difference between the ZAH (ZAH: heat affected area close to the weld) and the base material. With a low difference, polishing is easier. However, in the case of the prior art, the difference and the base material is higher quality machining and good steel known from the existing hardness between the ZAH region than 100 BH. The inventors have found that it is possible to modify the chemical composition of the steel such that the hardness difference is less than 50 BH while maintaining the desired hardenability. In addition, for suitable processing conditions, the microstructure of the ZAH region must be as fine as possible. Finally, welding must be carried out without cracking. These results resulted from the examination of the chemical composition such that on the one hand the ZAH region has a bainitic structure and, on the other hand, this bainitic structure has the least difference in hardness from that of the base material.

In order to further satisfy these conditions, it is particularly necessary to limit the content of non-carbide elements (e.g., manganese, nickel and silicon) by supplying a hardenable boron and increasing the content of carbide-forming elements such as vanadium, niobium and tantalum.

δ

More specifically, the chemical composition of the steel must be in wt.

following:

less than 0.27% carbon, but more than 0.17%, in order to obtain the required cavity wear resistance, the carbon content must in particular be between 0.2% and 0.24%, between 0.002% and 0.015% boron together with 0.005 % to 0.200% aluminum, and preferably at least one element selected between titanium and zirconium, the sum of the titanium content and half of the zirconium content is less than 0.3%, boron increases the hardenability without increasing the hardness difference between the ZAH and the base material; effect on hardenability but on the other hand somewhat increases brittleness, titanium and zirconium are intended to deoxidize steel and bind to nitrogen, an element that is always present, at least as an impurity to not react with boron,% to 3% molybdenum and hardenability, having molybdenum, wholly or partly replaced by tungsten, in the following amounts 0% <Mo + W / 2 <1.5% and preferably 0.5% <Mo + W / 2 <1.2%, accompanied by and preferably from 1.5 % to 2.5% chromium, tungsten am have a very favorable effect on the increased effect by boron interaction, low effect on thermal resistance, moreover, these elements reduce softening during annealing, which has a small difference in hardness between ZAH and base material and obtaining desired hardness after annealing above 500 ° C , on the other hand, with an excessive amount of molybdenum and tungsten segregate more firmly, which is disadvantageous for machinability and finishing, that is why the content is limited to 1.5% and preferably 1.2%, chromium is intended to increase the effect of molybdenum on hardenability and softening on ignition.

With these basic elements chromium, molybdenum and tungsten having a substantially basic effect, it is preferred that the chromium content is less than 1.5% when the amount of molybdenum and half the amount of tungsten is greater than 0.7%. This helps to maintain the desired softening resistance after annealing and to increase the thermal conductivity without reducing the hardenability.

For further annealing without loss of other properties, the steel may preferably contain at least one of the following elements: vanadium, niobium and tantalum in an amount corresponding to the sum of vanadium, half of niobium and a quarter of tantalum being between 0% and 0, 5% and preferably between 0% and 0.15%. These conditions also have the effect of reducing the hardness difference between the ZAH and the parent metal.

Furthermore, the possibility of obtaining a hardness greater than 250 BH after quenching and annealing to a temperature greater than 500 ° C, which is necessary to obtain the possibility of eliminating internal stresses or machining the surface of the cavity, is shown.

Cr + 3 X (Mo + W / 2) + 10 x (V + Nb / 2 + Ta / 4) > 2.1 and preferably for another possibility of increasing the annealing temperature and increasing the properties:

Cr + 3 x (Mo + W / 2) + 10 x (V + Nb / 2 + Ta / 4) > 3.6.

Finally, the repairability by welding can be greatly increased by adding titanium or zirconium added to the solidifying steel by dissolving titanium or zirconium oxides. In this case, titanium or zirconium forms very good nitride impurities that form a microstructure, and this has the advantage of increasing workability and increasing the thickness of the ZAH region as well as the base material. Increasing the width is an advantage of reducing welding cracks.

The supply of titanium or zirconium can be accomplished sequentially, for example, by supplying titanium or zirconium to a non-oxygenated liquid steel and then supplying a strong deoxidizer, such as aluminum, in an amount necessary to reduce the titanium or zirconium oxides formed. % Titanium, zirconium and nitrogen content by weight it must then be:

0.00003 <(Ti + Zr / 2) X (N) <0.0016

The nitrogen content, which depends on the production conditions of the steel, lies between several ppm and several hundred ppm.

In this process, the formation of coarse titanium or zirconium nitrides formed in liquid steel is limited. The steel obtained is then characterized by an amount of titanium or zirconium nitride precipitates of greater than 0.1 µm placed on a 1 mm ² solid microstructure of steel, four times less than the total sum of titanium nitride precipitates and half the total sum of zirconium precipitates % in the form of nitrides, expressed in thousandths. The steel thus obtained is then characterized not only by the presence of very fine nitrides but also by a small amount of coarse nitrides, which is advantageous for machinability and for polishability.

In addition to the above elements, the chemical composition also contains the following elements:

silicon intended for deoxidation of steel is an element which has a very disadvantageous effect, in particular on the thermal conductivity of the steel, and its content must be as low as possible, in any case less than 0.5% and preferably less than 0.2% and most preferably less than 0 , 1%, manganese, which increases hardenability and binds sulfur, but which has an adverse effect on thermal conductivity, is between 0% and 2% and preferably should be higher than 0.2%, especially when steel is desulphurized for improving its machinability, and not exceeding 1.8% to reduce the formation of segregates that impair machinability, preferably nickel between 0% and 2%, to increase hardenability, which element is expensive and not very suitable for good thermal conductivity, but is often present as a residual element in steels produced from ferrous waste, its content is preferably up to 0.5%, sulfur, also present in small amounts as an impurity, but may also be added In order to improve machinability, preferably in the presence of selenium or tellurium, it is necessary that the total sulfur, selenium and tellurium content is less than 0.2%, in particular not to deteriorate the polishability, preferably at least one lead and bismuth element such that the sum of their contents is less than or equal to 0.2% and preferably calcium in an amount less than or equal to 0.1%, all these accompanying elements are intended to improve machinability.

The remainder of the content is iron and manufacturing impurities. In particular, the impurities contain copper, in an amount which may be greater than 10% and which, in the presence of nickel, may affect the hardness.

In addition to the elements described herein, the chemical composition of the steel must satisfy two conditions, one relating to hardenability and the other to thermal resistance (opposite of thermal conductivity).

An exemplary chemical composition for satisfactory hardenability of steel must meet the following formula:

Qu = 3.8 x C + 1.1 x Mn + 0.7 x Ni + 0.6 x Cr + 1.6 x (Mo + + W / 2) + 0.6> kQu where kQu = 3 s preferably kQu = 4.

An exemplary chemical composition for satisfactory thermal conductivity of steel must meet the following formula:

R = 3.8 x C + 10 x Si + 3.3 x Mn + 2.4 x Ni + 1.4 x (Cr + Mo + W / 2) <kR, where kR = 11 and preferably kR = 9, (R is a number that changes in the same direction as the thermal resistance and thus in the opposite direction to the thermal conductivity).

By studying the above two formulas, it is apparent that the quenchability number Qu and the heat resistance number R differ in the direction, but their overall chemical composition selection may have maximum thermal conductivity at the same quenchability. Taking the total into account with additional constraints, the result is that the inventor has found that the chemical composition should be determined as follows:

R < 1.5 + 1.83 Qu which is very advantageous.

For steel intended for good repairability by welding, this chemical composition corresponding to the following formula is not appropriate:

AND

BH = 326 + 847.3 x C + 18.3 x Si - 8.6 x Mn - 12.5 x Cr <460

This is also not very desirable because these conditions simultaneously create a low carbon content which is not very suitable for cavity wear and high chromium and manganese which are disadvantageous for thermal conductivity and hardness similarity between the ZAH region and the parent metal. Therefore, it is advantageous if the composition of the steel is as follows:

BH = 326 + 847.3 x C + 18.3 x Si - 8.6 x Mn - 12.5 x Cr> 460

Before being used for mold making, the steel ingots obtained by rolling or forging are subjected to a heat treatment by quenching in air or water, depending on the thickness, and are then subjected to annealing to a temperature of more than 500 ° C and preferably to a temperature of greater than 500 ° C. 550 ° C, but lower than Ac 1. The purpose of this treatment is to obtain a martensitic or bainitic structure in the steel (the structure may also be martensitic-bainitic), substantially ferrite free (it would be desirable that ferrite is not present in any amount, with a small residual amount still present), and annealing to a temperature that essentially ensures the elimination of internal stresses and allows, if necessary, a surface treatment at a relatively high temperature. The annealing temperature is set to obtain a hardness comprised between 250 BH and 370 BH and preferably between 270 BH and 350 BH.

The steel of the present invention has particular advantages for the production of molds by a casting technique, a technology that makes it possible to obtain the molds by manufacturing from cast steel (not the wrought steel described above). According to this method, instead of machining, the cavity is obtained by casting in a massive block in which channels are formed for cooling by means of water circulation. The blank is made by casting and includes a mold cavity blank and outer portions having an approximate shape to provide the necessary mechanical strength, the walls of which are much thinner than those obtained when machining a cavity from a solid block. The mold itself is obtained by final machining of the semi-finished product and heat treatment. This machining has the advantage that it is much smaller than the machining required for solid block machining. On the other hand, the cast steel contains pores which must be removed by welding. The very good weldability of the steel according to the invention is therefore a very welcome advantage. Furthermore, the good thermal conductivity of the steel of the present invention represents another advantage in the possibility of reducing or even omitting cooling by circulating water in the channels passing through the mold wall. The advantage is the possibility of thinner mold walls. This allows the production of molds where cooling is performed by circulating gas around its outer surface. The heat treatment is identical to the heat treatment carried out on molds made of wrought steel, but must precede one or more of the austenitizations intended for grain refinement.

The following examples compare the steels A, B, C, D and E produced according to the present invention with the steels F, G, Η, I, J and K produced by known methods. The chemical composition (in% by weight) of these steels is shown in Table 1. Annealed quenched ingots with a bainitic or martensitic structure were made from these steels by rolling or forging. Their thickness, heat treatment conditions and properties obtained are given in Table 2 compared to those obtained for steels F, G, Η, I, J and K. In this Table the thicknesses are given in mm, the quenchability sizes Qu are dimensionless coefficients, thermal resistance magnitude R are dimensionless coefficients, thermal conductivity are given in W / m / K, hardness and hardness differences between ZAH and parent metal, H, are given in Brinella degrees, and BH is dimensionless coefficient.

Table 1

C Si Mn ~ Ni Cr Mo ~ ff Ί (B) Ti AND 0.215 0,045 0.420 0.210 2,320 0.790 - 0,047 0.003 23 (B) 0.215 0,045 1,030 0.220 2,290 0,815 - 0,002 0.003 52 * C 0.225 0.057 0.460 0.250 2,450 0.880 0.200 0.003 0.003 27 Mar: D 0.210 0.051 0.390 0.195 1,910 0.540 - 0,045 0.003 23 E 0.230 0.120 0.480 0.220 2,050 0.520 0.610 - 0.003 24 F 0.395 0.300 1,490 0.210 1,920 0.270 - - - - G 0.410 0.310 1,410 0,980 1,950 0.280 - - - - H 0.200 0.050 1,820 0.180 2,280 0.320 - 0.020 0.001 - AND 0.270 0.210 0.875 0.850 1,400 0.400 - 0.016 0.003 25 J 0.200 0,055 1,520 0,980 2,010 0.710 - 0.018 - - TO 0.265 0.325 0.850 0,835 1,420 0.410 - 0,035 0.003 23

* Zr not Ti

Furthermore, steels A, B, C, D and E contain approximately 0.020% aluminum and the titanium content is increased.

Table 2

th. sludge. annealing. Qu R vod. tvr. BH AND 140 air Mp 590 ° C 4.6 7.5 49 329 18 476 AND 400 water Mp 590 ° C 4.6 7.5 49 331 16 476 (B) 1100 water 600 [deg.] C 5.4 9.5 45 331 40 471 C 800 water Mp 590 ° C 5.1 8.3 47 313 48 483 D 210 water 575 ° C 3.9 6.5 51 313 15 Dec 478 E 150 air Mp 590 ° C 4.7 8.2 46 313 31 493 F 150 air 600 [deg.] C 4.8 12.9 38 329 110 629 G 700 water 600 [deg.] C 5.3 14.7 36 331 123 642 H 400 water Mp 590 ° C 4.6 11.3 41 313 80 452 AND 140 air Mp 590 ° C 4.6 10.5 42 299 50 533 J 800 water 510 ° C 5.3 12.5 39 331 76 458 TO 140 air 600 [deg.] C 4.6 11.6 40 295 51 531

These results show that all steels according to the invention have in these examples a thermal conductivity of greater than or equal to 45 W / m / K and a difference in hardness between the ZAH and the parent metal δΗ less than or equal to 45 Brinell, have a thermal conductivity less than or equal to 43 W / m / K and a difference in hardness between the ZAH and the parent metal δΗ greater than or equal to 50 Brinell. In particular, due to the small difference in hardness between the ZAH region and the parent metal, steels A to E have a weld-reparability which is noticeably better than for steels F to K.

By comparing the same hardenability and hence the maximum possible thickness, the advantages of the steels according to the invention are even more obvious, in the case of Qu = 4.6, steels A to E (according to the invention) have a thermal conductivity greater than or equal to 40 W / m / K and δΗ less than or equal to 31 degrees Brinalla, with steels I, H and K (as present) having a thermal conductivity less than or equal to 42 W / m / K and δΗ greater than or equal to 50 degrees Brinella. In the case of Qu> 5, steels B and C (according to the present invention) have a thermal conductivity greater than or equal to 45 W / m / K and δΗ less than or equal to 48 degrees Brinella, while steels J and G (according to the present state) have thermal a conductivity less than or equal to 39 W / m / K and a δΗ greater than or equal to 76 degrees Brinella. In both cases, the increase in thermal conductivity is greater than 9% and the reduction in δΗ greater than 37%.

It should be emphasized that the welding repair is preferably performed by supplying a material of the same composition as the parent metal. For this reason, the steel according to the invention can be produced not only in the form of ingots, but also in the form of welding wires or in the production of welding electrodes.

Industrial applicability

Said steel is particularly advantageous for molds made of plastic or rubber and preferably for materials whose melting point does not exceed 500 ° C.

Claims (10)

PATENT CLAIMS 1. Steel for the production of molds, especially casting molds injection molding, characterized by its chemical composition in % wt. η e following: 0.17 % < C < 0.27 % 0.0 % < Si < 0.5 % 0.0 % < Mn < 2,0 % 0.0 % < Her < 2,0 % 0.0 % < Cr < 3.0 % 0.0% < Mo + W / 2 <1.5 % 0.0% <v + Nb / 2 ! + Ta / 4 < 0.5% 0,002 % < B < 0.015 % 0.005% AlAl 0,2 0.200% preferably at least one of the elements sulfur, selenium and tellurium, in the total sum of these elements less than or equal to 0.2%, preferably at least one of the elements titanium and zirconium, in a content where the sum of titanium and half the zirconium content is less than or equal to 0,3%, - preferably at least one of the elements is lead and bismuth, in a content where the sum of these elements is less than or equal to 0.2%, - preferably the calcium content is less than or equal to 0.1%, the remainder being iron and manufacturing impurities, the chemical composition further corresponds to the following formula: Cr + 3 x (Mo + W / 2) + 10 x (V + Nb / 2 + Ta / 4) > 2.1 Mo + W / 2 > 0.7% when Cr < 1.5 QU = 3.8 X C + 1.1 X +η + 0.7 X Ni + 0.6 X Cr + 1.6 X (MO + W / 2) + 0.6> 3 R = 3.8 x C + 10 x Si + 3.3 x Mn + 2.4 x Ni + 1.4 x (Cr + Mo + W / 2) <11 Steel according to claim 1, characterized in that 0.20% C C 0,2 0.24%. Steel according to claim 1 or 2, characterized in that 1.5% Cr Cr% 2.5%. Steel according to claim 3, characterized in that 0.5% Mo Mo + W / 2 1,2 1.2%. Steel according to any one of claims 1 to 4, characterized in that the chemical composition corresponds to the formula: BH = 326 + 847.3 X C + 18.3 X Si - 8.6 X Mn - 12.5 X Cr> 460 Steel according to any one of claims 1 to 5, characterized in that the chemical composition corresponds to the formula: Cr + 3x (Mo + W / 2) + 10x (V + Nb / 2 + Ta / 4) > 3.6. Steel according to any one of claims 1 to 6, characterized in that Si <0.2%. of nahu- Steel according to any one of claims 1 to 7, characterized in that Si <0.1%. of n a č u - Steel according to any one of the preceding claims, characterized in that the titanium, zirconium and nitrogen contents are as follows: 0.00003 <(N) X (Ti + Zr / 2) <0.0016, wherein in the solid state the number of impurities of titanium or zirconium nitrides of greater than 0.1 µm, loaded in an area of 1 mm ^{2 of the} solid microstructure of the steel is four times less than the sum of the total impurity content of titanium nitrides and half the total content of zirconium impurities in the form of nitrides, representing thousandths in% by weight. 10. Steel according to claim 1, in y z n and č u j í c í s that its chemical composition IN % wt. is following: 0.20 % <c < 0.24 % 0.0 % <si < 0.1 % 0.0 % <Mn < 2,0 % 0.0 % <Ni < 0.5 % 1.5 % <Cr < 2.5 % 0.5% < Mo + W / 2 <1.2 % 0.0% <V - 4-Nb / 2 + Ta / 4 < 0.15 % 0,002 % <B < 0.015 % 0.005 % <Al < 0.200 % - preferably at least one of the elements sulfur, selenium and tellurium is less than or equal to 0.2% in the total sum of these elements, - preferably at least one of the elements titanium and zirconium in a content where the sum of the titanium and half the content of the zirconium is less than or equal to 0.3%, preferably at least one of the elements is lead and bismuth, equal to 0.2%, - _the calcium content is advantageously less than or equal to 0.1%, the remainder being iron and impurities associated with the production, the chemical composition furthermore satisfies the following relationship: Cr + 3x (Mo + W / 2) + 10x (V + Nb / 2 + Ta / 4)> 3.6 Qu> 3 R <1.5 + 1.83 Qu. Steel according to claim 10, characterized in that the titanium, zirconium and nitrogen contents are as follows: 0.00003 <(Ν) x (Ti + Zr / 2) <0.0016, wherein in the solid state the number of impurities of titanium or zirconium nitrides greater than 0.1 µm, loaded in an area of 1 mm ^{2 of the} solid microstructure of the steel is four times less than the sum of the total impurity content of titanium nitrides and half the total content of zirconium impurities in the form of nitrides, representing thousandths in% by weight. Use of a steel according to any one of claims 1 to 11, for the production of injection molds for plastics. Use of a steel according to any one of claims 1 to 11, for producing molds for plastics using casting techniques. Wire for welding or for the production of welding electrodes, characterized in that it comprises steel according to any one of claims 1 to 8 and 10.